GROWTH, MORPHOLOGICAL VARIATIONS OFTHE SHELL AND SOME BIOLOGICAL DATA OFTHE CONCH...

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GROWTH, MORPHOLOGICAL VARIATIONS OF THE SHELL AND SOME BIOLOGICAL DATA OF THE CONCH...

Article · January 1976

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GROWTH, M O R P H O W I C A L VARIATIONS OF

TEE SHELL

AND SOME BIOLOGICAL DATA OF THE CONCH ("COBO")

STROMBUS -

GIGAS

L.

(HOLLUSCA, WESOGASTROPODA)*

Pedro M. Alcolado

h s t i t u t e of Oceanography of

the Cuban

Academy

of

Sciences

i

Academia De Ciencias

De

Cuba I n s t i t u t o

De

Oceanologia

Serie Oceanologica No. 34

La IIabana, 1976

"fro

d e l

XX

Anversario d e l G r a m n a "

*

T h i s t r a n s l a t i o n funded by the Xallace Grovee Aquaculture Foundation.

Melody Ray-Culp

(3)

ABSTRACT

The present study was undertaken

in

nine locations along the north coast of Havana province; at the reefs located east and south of Batabano Gulf, Jardines de la Reina Archipelago and Cabo Crue (west coast of Oriente); in the period between May

1972

and May

1974.

The investigation deals with the influence of the environment on the growth rate of the queen conch (Strombus ginas, Linnaeus). Observed growth rates are between

4

and

8

cm per year. Shallow waters (less than 2 m deep) are better fit for rapid development. The morphology of the shell changes, according to the intensity of growth: large, light shells with numerous short spines and well defined spiral markings, are evidence

of

rapid growth. Growth is positively correlated with final size of the shell and negatively correlated with duration of the development period (juvenile stage).

Measures of population abundance, patterns of distribution and habitat The preliminary values of the mortality coeffi-

Other biological data are also given.

-___

-_____

characteristics are given.

cient are between 1.01 and 1.90.

(4)

TRANSLATOR'S

NOTES

(T/N)

--Some expressions are marked in parenthesis a8 it has been difficult express them in English.

--Conchs are localled called "cobo" in Cuba (an Indian aboriginal

name),

are not known

by

the same name in other Spanish-speaking countr

throughout the Caribbean.

--To

clarify some local Cuban ecological and/or environmental conditions a

T/N is given in parenthesis,

--"Medano" in Spanish means a sand flat or 'sand bank, shallow places; san bottom, sometimes level with water surface at low tide.

On

the

Cub;

coast, they are very extensive, separated from open ocean by coral reefs

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1

INTRODUCTION

Strombus gigas Linnaeus (Mollusca, Mesogas tropoa) , commonly called

*@cobof', is relatively abundant in the Antilles. Its culture possibilities have been mentioned by Iversen (19681, and its nutritional, medicinal and craft uses have beenmentioned by several authors familiar with the sea (Randall, 1963, 1964). This is the reason for the interest in the study of the biology of this organism.

Randall

(o p .

cit.) in his valuable contribution to the biology

of

the conch discusses among other things its growth, its reproduction and its biological relationship with other animkls. Little (1965) fills a great gap in the research of its anatomy. D'Asaro (1965) details the organogenesis of conch up to metamorphosis, and Robertson (1961) demonstrates its herbivorous feeding habits. Also, physiological, pharmacological, biochemical and other studies have been made; there is no need to mention them in the context of the present study.

Randall (op. cit.), the only one to work on the growth of the conch, In the present concludes that growth is slow (approximately

5

cm per year).

work, several locations are considered to.compare with his findings in the Virgin Islands. I have tried to tentatively associate the encountered differences in growth with environmental conditions. Also observed is the way the intensity of the growth rate (T/N: states "rhythm") is reflected in the morphology of the shell. At the same time, other biological information is

included here, some only in preliminary form.

MATERIAL

AND METHODS

After a diving inspection to several locations on the northwestern shelf and south

of

the island, zones were selected where different types of growth could be expected based on external morphological characters of the shell

(.

These will be described. In the

tables

and

graphs, the number

of

specimens are given for each sample made.

A total of

10,253

specimens were processed.

In

some cases, the samplings

were not a s intense

as desired,

for lack of time ox

lack

of

abundance

Sn

the zones selected,

or

because

of

several

interruptions

of the work.

Nonetheless

adequate

information

was

obtained.

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Different biotic and abiotic factors possibly related to aspect8 of conch biology were taken into consideration.

(A) Growth. The length measured is from the apex to siphonal canal (Pig.

1)

and was measured with a wooden device designed by the author.

The von Bertalanffy growth model was applied to data obtained in the tagging of

479

conchs in cove of the Institute of Oceanography. The Petersen direct method was applied to data from all locations. In those cases where the modalities representing the annual groups could not be identified by visual determination, the Harding

( 1 9 4 9 )

graphic method with probability paper was used.

L t - L L ,

=

length in time

Lt

La

=

maximum length

of

the species (theoretical) -K

d

decreasing coefficient

t =

duration of development (in time).

2m

initial theoretical time

With the annual increase of recorded length from tagged conchs recaptured in the cove

of

the Institute of Oceanography, the above growth parameters were determined.

Mean length arid annual increase in length were calculated by the Petersen direct method, assuming that the sequence of the modes is a one year interval and that recruitment becomes more intense in a relatively short and coincident length of time. This allows

for

the regreosion points of

von

Bertalanffy which correspond

t o t h e major

.lengths but not with the lesser ones. It is assumed

t h a t

larval recruitment takes place in July, and.that the first modal group

(of

smallest lerrgths)

sampled

in

J u l y

contained

one year

old specimens and the. second modal

group w a s

comprised

of two

year

old

conchs.

Prom

the

mean

lengths

of the modal. grcups we

can obtain

inetar,tzneous

growth rates

for

young conchs.

llnis method is hssed on

Randall's

( O F - cit.)

data which indicated

a

slight

spawning

incrcac-p.

i n A.prj.1

and May,

and t h e work of

D'Asaro (op. cit.)

who showed t h a t t h e dcrntioo r?f the lsrual p h a s e

is

about two

ponths under

I

aboratory

cn13d.i :.i.c*r,:.

'J.?trG!lgh t:?g,f:fnf;,

:->

: ?.= ('n-??. v o r i t t i w ~ s r f g ro wt h C O i l l d

be

f c l l n t - r d f r r q l J C ! n t f ? ; h r c ~ t . : - . i ? ~ , c f *-* : ...C-:>;T. 771 C;e.Lo C n i z : where 1 ! & 5 0 c ~ n r . 1 1 ~ were t a g g e d ,

(7)

Figure 1

Length considered in the growth study and measurements used to determine the length index. A

=

length of the body whorl, B

=

width of the body whorl.

(8)

* I I ,

3

growth v a r i a t i o n could be followed b u t less f r e q u e n t l y a t t h e same t i m e u s i n g t h e P e t e r s e n method f o r comparison w i t h t h e former one. Through t h i s method w e g o t a n i d e a of growth v a r i a t i o n s a t o t h e r l o c a t i o n s . The mean increase i n

growth r a t e o b t a i n e d through t a g g i n g f o r t h e d i f f e r e n t t i m e i n t e r v a l s w a s e s t a b l i s h e d from t h e l e n g t h d i f f e r e n c e s of conchs r e c a p t u r e d d u r i n g a p e r i o d . I n c a s e any conch was n o t r e c a p t u r e d d u r i n g a s p e c i f i c p e r i o d , b u t had been p r e v i o u s l y r e c a p t u r e d , t h e mean growth rates were s u b t r a c t e d through t h e i n t e r v a l s when i t could n o t b e measured.

...

The conchs i n t h e cove were tagged w i t h p l a s t i c numbered t a g s a t t a c h e d by bronze o r copper w i r e wound i n t h e s h e l l ' s s p i r a l . I n Cabo Cruz, n y l o n c o r d w a s used which i s e a s i l y s e a l e d w i t h a n a l c o h o l b u r n e r : t h i s l a t t e r form w a s much more e f f e c t i v e t h a n w i r e . Growth was s t u d i e d i n Cab0 Cruz, Diego P&ez Reefs ( A r r e c i f e s de Diego P g r e z ) , Cay0 A n c l i t a s , cove of t h e I n s t i t u t e of Oceanography and P l a y a Cubanacak, a l t h o u g h some t r i a l s were made i n Cay0 Matias and Cay0 R o s a r i o .

( b ) Length-weight r e l a t i o n s h i p . The specimens were weighed by s p r i n g b a l a n c e w i t h

2

5 g r p r e c i s i o n . b

was a p p l i e d where:

The a l l o m e t r i c l i n e a r r e g r e s s i o n model P = QL

P = weight

L = l e n g t h

Q = length-weight c o n s t a n t

b = exponent

Length-weight r e l a t i o n s h i p s were c o n s i d e r e d i n a l l a r e a s w i t h e x c e p t i o n of t h e Diego P&ez and Punta Arenas sand f l a t s (medanos i n l o c a l S p a n i s h ) and t h e Cayo Matias Reefs.

( c > Morphometrx. Q u a n t i t a t i v e and q u a l i t a t i v e m o r p h o l o g i c a l o b s e r v a t i o n s were made on s h e l l s i n each l o c a t i o n , O b s e r v a t i o n s were made on a parameter 1 w i l l c a l l " l e n g t h index"

(T/N

i n t h e o r i g i n a l i t s t a t e s " i n d i c e d e a l a r g a m i e n t o " = l e n g t h e n i n g index and t h e t r a n s l a t o r assumes it means

" l e n g t h index") which i s t h e r e l a t i o n s h i p between t h e l e n g t h of t h e body whorl and i t s maximum w i d t h . The l e n g t h i s mezsured from t h e midpoint between t h e two body whorl s p i n e s on t h e l e f t (having i h e a p e r t u r e o r mouth of t h e s h e l l f a c i n E you w i t t i t h e apex unpermost), and t n c Fxtreme end of t h e a n t e r i o r siphonal c a n a 7 . ?lie w;Clth 7 5 miasured from t f i 6 ' s n r e r i o r base of t h e s p i n e l o c a t e d OI-J ( h e ex:reme l e f t t o the b a s e rf t h P : ; ; q ~ 3 0 c a ~ e d On t h e extreme

(9)

4

I

3.

1 n e

S

1 : e

. L

>r

?t?

ne

r i g h t , through t h e a p e r t u r e ( o r mouth) of t h e s h e l l (Fig. 1). The f o l l o w i n g c h a r a c t e r s were a l s o taken i n t o account: i n c r e a s e i n d e p t h of t h e s p i r a l grooves, presence of knobs on t h e body whorl, s i z e and number of t h e s p i n e s per whorl ( i n t h e l a s t two whorls), e t c . These were observed i n a l l l o c a t i o n s under study. The samplings were n o t very e x t e n s i v e due t o t h e l a r g e u n i f o r m i t y observed i n t h e c h a r a c t e r s w i t h i n each l o c a t i o n .

( d ) Sex r a t i o . The s e x r a t i o w a s determined by t h e o b s e r v a t i o n of t h e g e n i t a l s . To do t h i s i t w a s necessary t o remove t h e animals from t h e i r s h e l l s . This s t u d y was made i n Cab0 Cruz and Diego Pe'rez Reefs.

( e ) P o p u l a t i o n d e n s i t y . P a r a l l e l t r a n s e c t s were made 100 m i n l e n g t h by 2 m wide, as widely d i s t r i b u t e d and homogeneous as could p o s s i b l y be done i n t h e areas under e v a l u a t i o n . The t r a n s e c t s were marked by a s t r o n g nylon cord 100 m long and t h e width was determined by a SCUBA d i v e r pushing a g l i d e r - t y p e d e v i c e t h a t marked 1 m of width. (This d e v i c e had knobs which were v i s u a l on t h e extreme ends, a p i s t o l - l i k e g r i p i n t h e mid-sub s u r f a c e with a p l a s t i c a n n o t a t i o n board on t o p , i n t h e c e n t e r ) . By t r a v e r s i n g a l o n g one s i d e of t h e nylon c o r d and back on t h e o t h e r throughout i t s whole l e n g t h , two 100 m a d j a c e n t areas were counted. I n t h e s e c o u n t s t h e p e r c e n t a g e of a d u l t specimens was c a l c u l a t e d f o r t h e zones under s t u d y i n t h i s manner (Cabo Cruz, Diego Pe'rez Reefs, Cayo Rosario Reefs and Cay0 Matias Reefs).

2

( f ) Weight p r o p o r t i o n of t h e e d i b l e p a r t s . The weight of t h e e d i b l e p a r t s as a percentage of t h e t o t a l weight (with t h e s h e l l ) w a s measured. The e d i b l e p a r t s were formed by t h e f o o t , f r e e of t h e v i s c e r a , mantle, e y e s , p r o b o s c i s , p e n i s and operculum. The weight of t h e whole animal, i n c l u d i n g i t s v i s c e r a l mass, b u t without t h e s h e l l , was a l s o measured. With t h e s e o b j e c t i v e s i n mind, samplings were made i n t h e cove of t h e I n s t i t u t e of Oceanography, Cab0 Cruz, Diego Perez Reefs and Diego P&ez sand banks.

( g > Time l e n g t h of s u r v i v a l o u t of t h e w a t e r . The conchs used were k e p t damp by s p r i n k l i n g them w i t h w a t e r . Excessive exposure t o t h e sun was minimized. The time i t took t h e conch t o lose i t s c a p a c i t y t o q u i c k l y r e t r a c t

i n response t o a s t i m u l u s (moment i n which i t h a s n o t l o s t i t s r e s t o r a t i o n c a p a b i l i t i e s once r e t u r n e d t o t h e s e a ) and t h e t i m e u n t i l i t d i e d w e r e compared. This was t r i e d in conchs i n Cabo Cruz a n d Cayo A n c l i t a s .

( h ) M o r t a l i t y . Takjnp i n t o c o n s i d e r a t j o n t h e specimens t h a t formed t h e f a s t two a n n u a l c l a ~ s e ~ il;n.r',i,ced by l i a r l i n t ' : w ; h o d ) and divided t h e number

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5

determined, where z

is

t h e t o t a l m o r t a l i t y c o e f f i c i e n t .

The l a s t two annual classes g e n e r a l l y are t h e only ones completely r e c r u i t e d i n t h e samplings, hence t h e estimates r e f e r only t o t h e l a s t y e a r of development. M o r t a l i t y c o e f f i c i e n t s were c a l c u l a t e d f o r conchs from Cab0 Cruz, Diego 'Pe'rez Reefs, Cay0 A n c l i t a s and Playa Cubanacdn.

I n Cab0 Cruz t h e m o r t a l i t y c o e f f i c i e n t w a s o b t a i n e d with t h e r e c a p t u r e of conchs tagged i n March 1973, one y e a r a f t e r being set f r e e . Of t h e 1,450 conchs t h a t were tagged, only 1,358 were used i n t h e c a l c u l a t i o n s s i n c e 14 l o s t t h e i r t a g s d u r i n g r e c a p t u r e processes and 78 were p r e v i o u s l y tagged i n November 1972.

AREAS

STUDIED

I n g e n e r a l , t h e breeding areas s t u d i e d were c h a r a c t e r i z e d by t h e predominance of j u v e n i l e s . These areas have p e c u l i a r g e o g r a p h i c a l c o n d i t i o n s , as w i l l be mentioned l a t e r .

Ecogeographicaz d e s c r i p t i o n s :

For each s t u d y area, only t h o s e environmental f a c t o r s which were i n v e s t i g a t e d w i l l be d e s c r i b e d i n d e t a i l .

( a ) Cove of t h e I n s t i t u t e of Oceanography (IDO) Location: 23O 05.5'M, 82' 28.5'W

This i s a small c o a s t a l e n t r a n c e p a r t i a l l y c l o s e d by two a r t i f i c i a l ramparts (made of c o n c r e t e ) w i t h an a r e a i s 1,500 m

.

I t s mean depth i s

I . 5 m. The bottom i s p a r t l y

s a n d y , muddy-sandy, with T h a l a s s i a and Syrinnodium and a few s c i t t e r e d rocks (in e r e a s ) .

2 The conchs i n h a b i t zones of 1 m o r less i n depth.

L l u i s R i e r a ( 1 3 7 2 ) s t a t e s t h e monthly average s a l i n i t y i s r e l a t i v e l y constant between 3 4 . 4 6 and 35.81°/oo. The oxygen undergoes c o n s i d e r a b l e annual and d i u r n a l v a r i a t i o n s . I t s c o n c e n t r a t i o n i s 3 . 4 - 5 . 4 ml/l d u r i n g t h e

~ ' T V T . P P S T ) V a n d 7 . S - 4 7 m l / l d r i r i n r t h e r a i n v F P R S O R . The d i f f e r e n c e b e t w e e r

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6

W e have observed t h a t , s t a r t i n g i n September, when t h e water temperature s t a r t s t o d e c l i n e , t h e t r a d e winds and n o r t h e r l y winds

(T/N

a t t h i s t i m e of t h e y e a r , v a r i a b l e and s t r o n g n o r t h e r l y

(NE,N,NW)

winds b e a t t h e n o r t h c o a s t of Cuba, and a r e l o c a l l y c a l l e d "brisotes") cause g r e a t water t u r b u l e n c e t h a t makes t h e water t u r b i d with a dark gray c o l o r and d i s a g r e e a b l e s m e l l . The winds d i s p e r s e t h e o r g a n i c d e t r i t u s i n t h e water column and d e s t r o y and remove a l g a e and p l a n t s . T h i s c o n d i t i o n a l t e r n a t e s with t h e calm s p e l l s and h i g h water t r a n s p a r e n c y d u r i n g t h e w i n t e r .

I n t h e cove, j u v e n i l e and a d u l t Strombus

ginas

show up, b u t n o t i n

( b ) Playa Cubanacih

Location: 23' 05.5'N, 80' 28.5"

The specimens t h a t were tagged and s e t f r e e i n t h e cove were c o l l e c t e d h e r e , t h i s zone being i n t h e immediate neighborhood of t h e cove. T h i s zone d i f f e r s from t h e former by being much more open; hence, t h e water change i s more e f f i c i e n t and r i v e r sediments do n o t s e t t l e . It a p p e a r s t o be r i c h e r i n a p p r e c i a b l e q u a n t i t i e s .

macrobenthic fauna as q u a n t i t i e s of j u v e n i l e 1 . 5 m and i s s e p a r a t e d p a r a l l e l t o t h e c o a s t .

( c ) Cabo Cruz

noted by t h e f r e q u e n t appearance of c o n s i d e r a b l e conchs. The a r e a s t u d i e d h a s a depth between 0 and from open w a t e r s by a rocky r e e f , s c a r c e l y 30 c m deep,

Q ~ ~ P c / ~ r -

,

" 5 v

O j L p c - Location: 19'

SO.~'N, 77*

4 4 . 5 ' ~

The study zone is l o c a t e d Ln a sandy r e e f lagoon which l i e s between t h e c o a s t , and a coastal. r e e f j o i n e d t o it on t h e e a s t and s e p a r a t e d by a s h a r p a n g l e on t h e w e s t . The r e e f s more than 2 km i n l e n g t h , a f f o r d s an e f f e c t i v e s h e l t e r f o r l i f e i n t h e lagoon. Seventy-three p e r c e n t of t h e wind comes from t h e e a s t , between n o r t h e a s t and s o u t h e a s t (Nationel A t l a s of Cuba, 1970). We were a b l e t o determine t h e e x i s t e n c e , in all o c c a p i m s , of an oceanic renewal c u r r e n t . A t times i t was s o intense t h z t to TOV ur swim s g a i n s t it wag very d i f f i c u l t . The d e p t h ranged froin 0 f.0 5 31.

The study a r e a W A S dis:ded i n t c t h r e e zi-.neb from e a s t t o west ( A , B and C) by i t s p h y s i c a l n ~ d b i u l o 2 3 c a l e i i c r a r t c z j s t i t r : the f i r s t and l a s t one w e r e

those O E i n t e i + s ! hexire i!,r

.

* % i c * L ~ ~ c w e , OR+ studied.

I, 1

The d t p r l , d: ,,alit 4 L' ' L f - % < , ? ) ':I 1 - n-. r 1, G : o ~ ? < 0.5 m , z n d zone C,

'I - i u i c r) thc f j z - s t , which , -

2 w. T i ? t t p - d t P ~ L ' ~ . . ' ~ Z F - ' v g t - 1 - 1 1 : A

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7

' i 1 .

gradually decrease with depth toward C. Thus, in September 1973, the average temperatures recorded were 32.5OC, 31.2 C and 3OoC in each zone, respectively, and in March, 3loC, 2 7 ' C and 26OC in the same order.

0

In zone

A

the sediment was coarse sand, with Thalasasia testudinum growing in association with algae of the genera Penicillus, Dictyote, Amphiroa and other coralline algae. There was an abundance of the coral Porites porties, the black sea urchin Diadema antillarum, and occasionally the white sea urchin Tripneustes ventricosus. Every time this shallow area was worked, a very strong east-weat current was noted. Great portions

of

this zone are exposed during low tide.

Zone B has turtle grass with scattered corals, populated with Diadema antillarum. Macroscopic algae was not abundant, only small epiphytic algae over Thalassia and rocks.

Zone C was mud/sand, with some areas 'populated with Thalassia, others without,

but

containing patches totally covered by filamentous algae (ceremials and cladophorals) from which conchs feed.

On

several occasions it was observed that great quantities

of

rhodophicean algae were detached from extensive areas of the bottom. The accompanying macrobenthic fauna included Petrochvrus diogenes, Diadema antillarum, Strombus costatus, some annelids

(polychaetes) and a few Cassis tuberosa, etc.

(d)

Location: 2 2 ' 02.01N, 8 1 ' 31.8'W

This area comprises an extensive turtle grass shallow protected by a mile long barrier reef separating it from Golfo de Cazones. This reef is interrupted on its northern third by a canal (T/N in Cuban Spanish these are called "quebrados"

Diego P&ez Reefs (Arrecifes Dieao Pgrez)

broken, meaning possible entrance for small vessels).

The northern area (zone

A)

has a depth of about 3

m

in the sampling section, and the southern third (zone B) has a depth of 4 m.

Salinity variee between

35.0

and 36.2O/oo (Lluis Riera, 1972) with

a

minimum temperature

in

winter

of 2 5 . 5 O C and

a summer maximum

of

31.5

C

(Emilsson and Tapanes,

19?1). In

general,

algae a r e

scarce, especially those

t h a t may be food

for the conchs, except

in

zone

A ,

where

in

May 1973

some filamenious algae were o b s e r v e d . %e s c a r c e species

of macroscopic algae are

P c n i c S l j u s , Avrainvillen a n d Halimedq. Jri f o n t r P s t , the bottom is

denbely

c o v e r ( 2 b y l'rralas:.fa Toe dc-cmnpariying ~ L L I I . ~ i s ab u n d an t a n d is formed by

0

(13)

8

great nmbers of Strombus costatus and Meoma ventricosa, which are herbivorous. Some Cassia flammea, Oreaster reticulatus, Rolothuroidea, and

the sponge Cliona sp., were observed intensively boring the conch shells.

(e)

Location:

22O

27.O'N,

81'

33.7'W

This sand bank is divided with an area of mud and sand and another of coarse almost rocky sand, not exceeding

a

depth of 0.3 m, which is why collections were made by wading as was done in zone

A

at Cabo Cruz. The bank forms a belt almost

50

m wide around a coastal mangrove, and apparently receives a slow current from Golfo de Cazones. The algae Amphiroa fragilissima was observed,

as

well as other small algae growing over Thalassia. In the accompanying fauna the following were seen: Cassis tuberosa, Pasciolaria tulipa, and Petrochyrus diogenes, the latter one living in conch shells.

Dieno Pdrez sand bank (MLdano de Cavo Diepo Pdrezl

( f )

Location:

22O

10.7'N,

81° 35.o'W

This area is very similar to the former in all aspects except that Strambus gigas is not abundant. This location receives water from the most remote region of Golfo de Cazones, south of the islands.

Punta Arenas sand bank (Midano de Punta Arenas)

( g )

Cavo Anclitas

Location:

20' 48.5'N, 7

8 ' 56.5'W

This place follows the same pattern of the two previous ones; it is a large zone of

0.3

m depth extending along the coast. It extends offshore to almost

50

m from the mainland and deepens until reaching the open Caribbean Sea. It has an abundant sediment of mud and sand with Thalassia testudinum.

This area tends to become very warm in summer as

was

recorded in

J u l y

1973.

The observed algae are: Amphiroa sp., Laurencia

~ p . ,

Acanthophora sp.

and

Gracilatia

sp. As

accompanying fauna we found a

f e w C a s s i s

tuberosa, Strombus raninus and Petrochyrus dioxenes.

(11)

C a w Rosario)

Cay0 Matfas and Cay0 Rosario Reefs (Arrecifes

de

Cay0 Matias

Location:

21' 33'N, 82* 29.7'W and 21° 36.b'N, 81' 56.0'W

These are reef lagoons very s i m i l s r to t h o s e of Diego P e r e z . In the

(14)

9

( i ) Cay0 Flamenco

L o c a t i o n : 22' 01.7'N,

81°

34.5'W

The c o l l e c t i o n w a s t u r t l e g r a s s found a t a mean d e p t h of 1 m a d j a c e n t t o t h e key. '

RESULTS

AND DISCUSSION

I . Growth

1.1 Growth i n l e n g t h . The growth i n l e n g t h of Strombus gigas v a r i e s c o n s i d e r a b l y i n r e g a r d t o t h e l o c a l e c o l o g i c a l c o n d i t i o n s . I n t h e p r e s e n t s t u d y many d i f f e r e n c e s were r e c o r d e d , w i t h mean growth v a l u e s t h a t r a n g e from 4 cm t o 8 cm p e r y e a r . R a n d a l l (op. c i t . ) i n h i s s t u d y i n t h e V i r g i n I s l a n d s , showed a growth r a t e of approximately 5 c m p e r y e a r , v e r y s i m i l a r t o t h o s e r e c o r d e d i n t h i s s t u d y f o r l o c a t i o n s where growth i s slow.

The c u r v e s c a l c u l a t e d through von B e r t a l a n f f y ' s e q u a t i o n a g r e e w e l l w i t h t h e conch growth, hence they provide a good means of e s t i m a t i n g t h e a g e when s e x u a l m a t u r i t y o c c u r s , a t which time growth s t o p s ( P i g . 2 ) . The maximum l e n g t h (Lo h a s o n l y a t h e o r e t i c a l v a l u e f o r a mathematical f u n c t i o n i n o r d e r t o develop t h e growth c u r v e . The mean v a l u e f o r t i s -0.09/year (growth p a r a m e t e r s a r e g i v e n i n T a b l e 1 ) .

0

The d i r e c t method of P e t e r s e n was v e r y e f f e c t i v e i n t h i s work. The f a c t t h a t t h e modes are c l e a r l y observed shows t h a t t h e r e c r u i t m e n t i s i n t e n s e Over a s h o r t p e r i o d of t i m e . Without t h e need t o g e t a l a r g e sample, t h e r e s u l t s have been c l e a r l y r e c o r d e d . I n l o c a t i o n s of low p o p u l a t i o n d e n s i t y , 2 0 specimens were enough t o o b t a i n a mode. I n F i g s . 2 and 6 w e c a n d e m o n s t r a t e t h e p e r f e c t c o i n c i d e n c e of P e t e r s e n ' s method w i t h t h e troublesome t a g g i n g i n Cab0 Cruz

.

I n t h e polymodal d i s t r i b u t i o n i n zone A of Cabo Cruz, i n March 1974, t h e f a l s e mode of ! 9 . 5 c m w a s not c o n s i d e r e d as it does n o t a g r e e w i t h t h e r e s t of t h e o b s e r v a t i o n s ( F i g . 3 ) . I n t h i s zone t h e mean growth r a t e was 8.1 c m p e r yea1 I tbe h i g h e s t r e c o r d e d .

*

Xn t h e l a s t two samples taken i n zone B of Diego P e r e z (Fig. 3 ) , a

i t ! X a t j . ~ c ~ l y weak mode appear- (B), 'and as i t was repeated ir. b o t h , i t is c(\nC;iE~~rt~ci v e i i d . T h e g r o v t h c u r v e s based on t h e s e d a t a s u p i j o r t t h i 8 idea.

' j h f :L:-;..J'-J n f P p e c i m n s g r i l > i S yeer c-Lnss may be C u e

r e

a i e d u c t i n n i n t h e

' 0 - , - 8 ' l J : t ~ ~ ' > . . ~ .

(15)

QModal lengths in cove of Ocean. I n s t i t u t e

@Modal lengths i n Cay0 Anclitas

-...- Theoretical growth curve i n cove o f Ocean. I n o t i . ---Theoretical growth curve i n C . A n c l i t a s

-Temporal w a y of grouth i n cove of Ocean. I n o t i .

3- Length o f conchs c o l l e c t e d i n cove.

(16)

. -. . . . . . . . . . I . . . . . _. .. - - - . ...

~ .~ .-

TABLX No. 1

Growth Time = years length

=

cm Length-weight re3 ationship Mean

L o c a ~ i on

ii

k.L=

L m

to

S?

S:k rate b S2b

log Q $103

Q

r n

( . I ! - , , C:.Iii A -0.330 11.66 38.34 -0.05 0.312 0.0023 8.1 3.35201 .0.91 0.30 -2.51331 0.89 65

( r ~ h C J - ~ J Z ) I3 -0.287 1(?.91 35.06 -4.12 0.701 O.CW33 7.6 3.05476 1.02 0.29 -2.94697 0.99 113 D I { - ~ I ) PL+VL A -0.429 9.9Y 23.27 4 . 0 9 0.562 ll.~’ro.~S 5.2 3.62715 1.08 0.25 -2.38685 0.99 3 4

f . ~ ~ ~ * y ~ j P ~ - I ~ : z H -0.432 9.19 20.76 4 . 0 9 0.319 0.0023 4.3 3.28912 0.97 0.32 -2.81601 0.93 1S1

( - ‘ , I \ I I \ilcir!i\> -0.571 13.84 25.98 0.09 0.349 O.Ot\29 7.0 3.46839 1.01 0.21 -2.42601 0.99 112

I< .>ci;t 1 !i \ t i I I I I o

3 .

; ’,‘,L’;’ t i ! J ! c ~ ~ : ~ : t -0.360 1 2 . 4 1 33510 0.13 1.232’ 0.0890f 7.5 3.38134 1.08 0.45 -2.63056 0.96 63

P I ;1 , , ; I

<

I I 0 , I I1;IC < I 1 1 . 0.185’ 9.e.f” 521.30” 4 . 0 5 “ 0.278” 0.0052” 7.7 3.31059 1.04 0.43 -2.60597 0.82 93

Rosario

- - -

_.

- m 4

3.62869 1.04 0.20 -2.43759 0.95 1-17

“ b

A

- -

- - - - -

..:A

- - -

( . a \ ( ) .L?3ti3s

-

i‘’)

These variations have higher values as the estimates were made starting

from individual markings of 41 recaptured conchs.

by d i r e c t method.)

(The rest were obtained

i c

W e have no confidence in these values.

~2 Variation r = correlation of coefficients

(17)
(18)

10 . - *

The growth rates i n both zones of t h e Diego Perez Reefs

were

t h e lowest (4 c m p e r y e a r i n zone

B

and 5 cm per y e a r i n zone A).

I n Cay0 A n c l i t a s w e have a coincidence i n t h e v a l u e of t h e y e a r class, r e p r e s e n t e d by t h e mode of

B

with t h a t of zone A i n Cab0 Crue, r e p o r t e d only a few days b e f o r e . The f i r s t mode i n Cay0 Anclitas i s n o t clear, t h e r e f o r e a n approximate estimate i s given and p o s s i b l y t h e real v a l u e i s less due t o t h e d i s p e r s i o n observed i n t h e lower v a l u e s of t h e frequency d i s t r i b u t i o n . The l a s t y e a r c l a s s i s masked by t h e second, t h e r e f o r e E a r d i n g ' s method should be used t o i s o l a t e i t . The e x i s t e n c e of t h e l a s t class i s j u s t i f i e d because i t i s composed of i n d i v i d u a l s which show s i g n s of beginning s e x u a l m a t u r i t y ( c r e n a t i o n and l i g h t expansion of t h e o u t e r s h e l l l i p ) , which d e f i n i t e l y s e p a r a t e s i t from t h e previous c l a s s .

The s i m i l a r i t y of t h e l a s t two modes may be due t o t h e f a c t t h a t t h e t h i r d y e a r c l a s s w a s f i n i s h i n g i t s m a t u r a t i o n p r o c e s s , hence i t had stopped growth a few months b e f o r e . Consequently, t h e growth i n l e n g t h i n t h e l a s t p e r i o d may have been underestimated.

I n Cay0 Rosario and Cayo Matias, i t i s f e l t t h a t growth follows a p a t t e r n s i m i l a r t o t h a t of zone

B

of Diego Pdree, as t h e modes of t h e t h i r d y e a r c l a s s of t h e August sampling ( t h e only ones appearing i n both of t h e f i r s t l o c a t i o n s ) c o i n c i d e and t h e morphological c h a r a c t e r s of t h e s h e l l are s i m i l a r and a r e r e f l e c t e d i n t h e growth rhythm ( P i g . 3 ) . The younger y e a r c l a s s e s were n o t found, as t h e samplings were made i n one end of e a c h lagoon, where t h e p r o b a b i l i t y of f i n d i n g j u v e n i l e s diminishes. The same t h i n g happened i n t h e f i r s t sample taken i n zone B of Diego Pe/rez.

Unfortunately w e do n o t have d a t a from Playa Cubanacan on specimens of modes of l e n g t h over 1 7 cm. Thus f o r t h e v a l u e s a t hand, t h e growth e q u a t i o n shows a s t r a i g h t l i n e which would have happened w i t h t h e growth c u r v e s of t h e cove of t h e I n s t i t u t e of Oceanography i f l a r g e r mode l e n g t h s had n o t been recorded. This almost l i n e a r form of growth cannot be accepted as p r o b a b l e , and w e p r e f e r t o assume t h a t t h e a d u l t s t a g e i s reached by t h e conchs i n t h e c m e a t t h r e e y e a r s of age, although i t may be one o r two months e a r l i e r . ' h e r e f o r e we decided t o r e p r e s e n t growth as i t i s shown t h e r e ( F i g . 2 ) .

Tht d a t a used t o c a l c u l a t e t h e growth e q u a t i o n s a r e shown i n Tables 2 , 3

.-??IS 4

1

:

'f-l-5: s i r e o f t h P P h e l l and d u r a t i o n of t h e g r o w t h period. P l o t t i n g ri P ~ ~ - ' P T ~ E m e ~ r l I g ~ o v t h r a t e s (TI a g a i n s t t h e a d u l t l e n g t h ( L measured j n

t

(19)

TABLE 2 Modal lengths

Location Sample Date A B C D n

19 41 45

1 2-111-3973

-

16.0

- -

2 29-V1-1973 I 15.5

- -

3 29-IX-1973 12.8 20.8

- -

Cabo Cruz A

4 21-111-1974 16.0 22.0

-

_I 42

1 201X-1972

-

12.6 18.0

-

1 69

2 18-Xi-1972

-

13.0 19.5

-

78

3 29-1 11-1973

-

14.5 21.0

-

712

16.2 20.8

-

135

4 29-v1-1973

-

5 29-IX-1973 11.8 18.6

- -

985

.

6 20-JII-I974 14.5

21.5 -

_. 478

Cabo

Cruz C

1 18-X-1973 7.7 13.3 17.0

-

278

2 19-XII-I973 10.3 14.3 17.3

- 1

063

Diego PCtrz A

1 8- I X- 1972

-

_. 13.5 16.5 104

104 222 Diego P4rez

B

2 18-V- I973 6.8 12.5 15.5

-

3 27-VII f-1973 9.0 13.8 15.8

-

___ -

7.5 17.5

-

20

8.5

-

I 29

Playa Cubanacin

3 15-VII-1972

-

9.5 18.5

-

50

59 29

1 29-1’- 1972

-

2 29-VI-1972

-

4 7-111-1973 _. 15.0

- -

5 30-V-1973

-

17.0

-

_.

14

1

C a p Ancli tas 1-VII-1973 11.5 18.5 21.5

-

*

Cayo Rosario 1

23-VIlI-1973

- ’

- 15.6 -

217

16.5

- 29

Czyo Matfas 1 25-VIII-73

- -

12.0

- -

79

99

.l 28-VIII-72

-

2 15-X-1972

-

12.2

- -

-

125 88 108 3 30-XI-1972

-

13.5

- -

‘ove O f

the

4 29-xl1-1972

-

13.8

-

Ocean. Instl.

j 29-11-1973

-

15.0

- -

26 125 118 136

82

47

26 6 Y-IV-1.973

-

15.5

- -

7 9-v- I973

-

16.0

- -

8 11-VJ-1973

-

17.0

- -

9 12-V1J-1973

-

18.0

- -

10 z - c ‘ i r i 1971

-

19.0

- -

1 1 14-?iI1*1973

-

1?.5

- -

12. 21.11-1974

--

211.5

- - -

(20)

TABLE 3

Estimates of growth rates for different mean lengths deducted from polymodal distribution

Samples Modal Rates - L (cm/yr)

Location Considered Considered t(cm) t

.)

Caho Crux A 3 A - B 16.8 8.0

I 2 3 4 5 1 - 5

6 2 - 6

B . - C B - C B - C B - X:

A - B B - B

A - - B B - B

15.3 16.3 17.8 ' 18.5 15.2 15.6 18.0 18.0

. . 5.4

6.5 6.5 4.6 6.8 6 .O 7.0 7

.O

1

n

-. B

1o.s

5.6

I

u -- c*

15.1 3.7

A - c

A --* B

12.4 12.3

4.7 4.0

2 B - C 15.8 3

.O

2 A - C 13.8 3.5

1 2 2 2 Dicgo P 6 i w B 3

3

.

1 - 3 3

C - D 15.0 A - B 9.7 B - C 14.0

A - c .

11.0 A - B 10.9 B - c 14.4 .

iz

- c

12.4

c - c

13.7

3 .O 5.7 3 .O 4.2 3.8 * 2.8

,

3.4 2.3

1 B - C 10.0 10.0

Pla\,a Ciilxiiiachti 3 B - C 8.8 8.8 1 - 5 13 - B 9.5 9.5

1 1

A - B

R

-- c

20.0 15.0

7

3 .O .O

(21)

TABLE 4

Estimates of growth rates for different mean lengths deducted from annual classes

Estim. age - L (cm/yr)

Location Sample Mode L(cm) (years) L(cm) t

Cab0

Cruz A 2 A 12.8

-

1.2 5.3 10.7

3

B

18.5 2.0 9.3 9 3 .

cab cnu. c

3 2 A B 11.8 16.2 2 1.2

.o

4.9 8.1 9.8 8.1

~-

I h 7.7 0.9 4.3 8 -6

Diego P6rez A 1 B 13.3 1.9 7.0

7

.O

1

C

17.0 2.9 8.8 5.8

1 A 6.8 0.9 3.8 7.6

Diego

PCrez

C 1

B

12.6 1.9 6.6 6.6

1

C

15.2 2.9 7.9 5.2

1 A 12.0 1

.o

6

.O

12.0

Cay0 AncIitas I

B

18.5 2.0 9.3 9.3

1

c

21.5 3.0 10.8 7.2

-

Playa Cubanacan

-

3 3

A 9.5 1

.o

4.8 9.5

B 18.3 1

.o

9.2 9.2

Cayo Matias 1

c

15.6 3.1 7.5 5

.o

Cay0 Rosario 1

C

16.5 3.1

8 .O

5.3

(22)

11

the same zones, a parabolic relation resulted between both parameters. Thus we have nine points to which a given c u m e can be acceptably fit 'by the equation :

-0.208 (Lt-14.

39)

T - 9 . 7 1 - e

where 9.7 is the estimated theoretical maximum rate of growth of the species

(T

) $ 14.39 is the intersection point of the curve with abscissa

(L

) and

-0.208 is a constant

(-K)

(Fig.

4).

0

With this curve the mean growth rate can be estimated starting from the average length of adults collected at random. This equation should be used with some skepticism due to

the few

locations that were studied.

Unfortunately we cannot include the results of Randall ( o p . cit.) because the adults he measured were collected at

9

m (30 feet) depth, while his growth study was made at .2 m depth with conchs collected

in

another location not mentioned by him. It is clear that the adults whose mean length we estimated were collected in the same place where the juveniles used in the investigation of development were located. The validity of the mathematical expression of relationship between growth and final length at the present time is considered to be limited to zones of our latitude and between depths ranges from

0

to

4

m.

Nevertheless, the most important thing is that the positive relationship between both parameters is well demonstrated.

If the L values are taken from each location and are divided between their corresponding

T,

we get the different time periods at which development culminates in each one of them. Plotting i t against

L

we have a curve that

t

suggests the possibility that the conch cannot reach sexual maturity before three years (Pig. 4). This could cast doubt on Iveteen's (op. cit.) report on what some investigators of the University of Pennsylvania stated concerning the possibility that the conch could attain sexual maturity in two years.

t

1.3 Growth in weight. Through the equation that describes the length- weight relationship and the one for the von Bertalanffy growth model, the growth in veight of some organisms can be deduced. Through this method the growth curves in weight CBR be calculated for the conch. In Table 1 we

(23)

e h 't :d m

I f

.a

I.

P

n t

t e t

P

0 0 /

c

I i

Figure 4

Relationship between the mean growth rate (T) and the final average length (L) in the locations studied, represented by the long dash line. Relationship bewteen the average final length and the time when they become adult,

the short dash line. The l i r l e crossing vertically in 6 gives

the probable range of

T

and L for the location. represented by

(24)

12

observed i n t h i s l a s t a s p e c t are principally determined by l i g h t n e s s of the s h e l l , e s p e c i a l l y i f w e take i n t o account t h a t

t h e r e l a t i v e the we'ight of t h e s h e l l r e p r e s e n t s about 80% of t h e t o t a l weight, as w e may see i n the following d e t a i l 8 (Fig. 5 ) .

1.4 Annual method of growth. The conch8 show marked v a r i a t i o n s i n growth between s t a t i o n s . Overall, we observed a r a p i d growth period t h a t occurs from May t o September and a period of slow growth during t h e rest of t h e y e a r (Fig. 6 ) .

Without doubt, temperature a s one of t h e f a c t o r s t h a t c o n t r o l t h i s v a r i a t i o n , h a s g r e a t importance as i t increases t h e ailmentary and metabolic rhythm of poiklothercuic organisms. Although i n t h e watmer months h i g h e r rates are r e g i s t e r e d , i n t h e cove t h e r e i s no p e r f e c t p a r a l l e l i s m between t h e s e and t h e temperature. .When

w e

record t h e decrease of temperature during t h e months of September, October and even i n November, i n which it may be equal o r above t h e one i n May, we observe t h a t the growth during t h e s e months i s low. I n t h e cave, t h i s f a c t could be explained i f w e t a k e i n t o account the e f f e c t of p o l l u t i o n and contaminated waters from QuibdRiver which had been f e l t with g r e a t e r i n t e n s i t y s i n c e mid-August during the study y e a r s . This was t h e cause of the loss of g r e a t q u a n t i t i e s of d e l i c a t e a l g a e , which probably diminished the oxygen content producing t h e occasional death of organisms, including conchs.

In t h e cove, a l g a e were abundant i n 1973 and 1974 s i n c e mid-March;

n e v e r t h e l e s s , t h e growth r a t e i n March and April during those y e a r s w a s very low. Therefore, w e can deduce t h a t although food i s t h e p r i n c i p a l base f o r good development, i t is not t h e one t o determine the growth during a given month period.

During the c o l d ' months, low temperatures a c t n e g a t i v e l y on metabolism hence the slow growth r e g i s t e r e d . I n the cove w e had o t h e r s p e c i f i c f a c t o r t h a t g r e a t l y decreaeed t h e growth rate, such a s water turbulence, t h e scouring of algae by wave a c t i o n , the g r e a t t u r b i d i t y of w a t e r produced by s t r o n g wave a c t i o n ( b r e a k e r s ) t h a t s t a r t e d i n September in both y e a r s and continued almost throughout the winter period of 1972 and 1 973. This causes d i s p e r s i o n of organic contaminants ( c x f , 6 t ? i c F C ~ Z L U ~ : ' O L I ) brought i n by t h e river throughout the waLer c o l u m d u e :n the instability o f :he s e d i m e n t . ?I: F i g . 7 , an overall o l - s e r v a t i c n w i 7 1 show t h e ind<rert. i n ! :lyetice GI, growth i n t h e cove O F

(25)

T

t i

.'

/

r' '+ I

t / +

# /

+

I

I

/

+ /

+

9 d +

*.+ r f

/ o f

/

4 .

f

/ +

+,'

+

Q

++/

Oiego pdrer Zona B

+

C O ~ O

Cruz

Zona

c

t I l i ~ ; ~ , , , I I ,

12 13 14 15 16 I f 18 13 20 21 22 23 24

(cm)

-

..1 .

-

. . I : ' I /

.

F i g u r e

5

K e l a t i o n s h i p b e t w e e n length and w e i g h t - of thcd cci-tch and of empt.y s h e l l s . T h e c u r v e frorn knc ' f i t a s Key doe:. iwt a p p e s r h u t i s v e r y c ; ;,ri 1 a r to t h a t c f Cuben;:cCj> Eeacli

.

(26)

1 :

..-d

!

I

...

r -i--

. i

--- C. Crua, Zone C (Petersen method)

----.---.. C. Cruz, Zone C (Marcaciones)

-...-

D. Pdrez, Zone B (Petersen)

-- Cubanacgn Beach (Petersen method)

- Institute Cove (Marcaciones)

-.

-. Virgin Islands (Randall, 1964)

---

... **...*-...-

.-.

I

r L .-.-.-.-.-

I

- 1 - .

J

1

%-VI

'

V I I i v l l l ' I X x

'

X I

'

X t l

I

I I I t I I l l I V V Y t VII

'

V I I I ' I X

x '

X I

'

XI1

I

I

'

I I I

I I I Y '

Months

Figure 6

P r n v i s i o n a l representation of the growth rate in different-1.ocations.

(27)

-

XI1

115747-

Rate of growth in Inst, Water temperature

Precipitation

Days of rain in the period Number of recaptured tagged

samples

Cove

Figure 7

n a l representation of the growth rate in the cove of the Oceanographic

Institute in regard to rain and temperature.

Afbeelding

Updating...

Referenties

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